The invention relates to surgical procedures on the anterior aspect of the cornea of the eye. Such procedures include the operation of lamellar keratoplasty, designed to remove scarred, irregular or opaque corneal tissue from across the visually critical central optic zone of the cornea and replacement with a partial donor cornea to restore the corneal shape and clarity, thereby improving vision. It relates also to other operations on the anterior cornea designed primarily to produce changes in the optical imaging of the cornea, thereby correcting optic errors of the eye, such as myopia (nearsightedness), hyperopia (farsightedness), astigmatism, optical aberrations and combinations thereof.
The operation of partial thickness lamellar keratoplasty to remove corneal opacities has been practiced for many years (see Brightbill, FS, Corneal Surgery, Chapter 33, C.V. Mosby Co., St. Louis, 1986). It has classically been performed by direct mechanical removal of a circular disc of tissue of constant thickness and replacement thereof with a similarly shaped piece of donor corneal tissue. The optical quality of the final cornea has frequently been known to be irregular or with some interface opacity, and often results in reduction of vision from normal. More recently, this procedure has been performed with a high-speed microkeratome to effect detachment of the anterior disk both from the patient's cornea and from the donor's cornea.
Barraquer teaches the general art of altering the anterior corneal curvature of the eye to effect changes in refraction, or optical imaging of the eye, with the operation of keratomileusis, a form of lamellar keratoplasty. (See IBID, Chpt. 37). In this procedure, a circular lamellar disc of constant thickness centered on the visual axis is removed from the front of the patient's cornea with a high-speed microkeratome. Following said removal, called a lamellar keratectomy, the resected lamellar disc of constant thickness is placed onto one of two available devices (Barraquer cryolathe, BKS device) to effect modification in shape to produce a lenticule with refractive optical power. Although operationally different, both devices effect the production of a refractive corneal lenticule. The lenticule is produced by volumetric mechanical removal of stromal tissue from the cut and exposed corneal stromal surface of the resected lamellar disc. Such tissue removal may be greatest in the center of the disc, which allows for correction of myopia, or toward the outer periphery, which allows for correction of hyperopia. In any event, the tissue removal is usually such that there is a smooth and regular transition of thickness as one traverses the optically modified (optic zone) area. Following tissue removal from the disc (now called a lenticule), it is replaced onto the patient's cut stromal surface remaining behind after the initial keratectomy. Said replacement results in a new anterior corneal curvature and alteration in the optic imaging of light by the cornea.
The inventor teaches the possibility of accomplishing the same while utilizing donor corneal tissue to receive the volumetric optic cut. This allows for the tissue lenses to be manufactured in advance by someone other than the operating surgeon.
U.S. Pat. No. 4,732,148, L'Esperance, issued Mar, 22, 1988, discloses a method of applying ultraviolet radiation to the anterior cornea (photorefractive keratectomy) in order to correct the optical errors of myopia, hyperopia, and astigmatism. Unfortunately, the delicate anterior membrane complex of the patient's cornea (primarily Bowman's membrane) is destroyed in the process, leaving a cornea which is anatomically, and perhaps physiologically, abnormal. In addition, two other drawbacks of this method have been noted. The first is the production of haze within the operated cornea, which lasts for months, and which may be associated with visual symptoms or reduction in vision. Second, the anatomically abnormal cornea develops a healing response such that the outermost epithelial layer, regenerated over the operated area from peripheral unoperated epithelium, frequently demonstrates hyperplasia or thickening postoperatively. This can cause gross inaccuracy or instability of the obtained optical result.
Furthermore, it discloses a method of performing a corneal transplant operation with an ultraviolet laser, using donor tissue, whereby a refractive error may be simultaneously corrected, In this approach, laser irradiation is applied in a constant fashion to the anterior cornea of the patient such that a circular disc of constant thickness is ablated. A disc of comparable diameter but greater thickness is fashioned from a human donor cornea, with the anterior membrane complex intact. The donor disc is then placed into the recipient opening and sutured. Following this, the laser is applied to the front surface of the donor cornea, now part of the patient's cornea, and some of the front surface removed until the donor disc no longer protrudes above the patient's cornea. Also, optical power may be altered by ablating the front of the donor disc in a fashion that selectively alters the thickness of the donor disc in a controlled way. This method, also, has the undesirable result of damage to the anterior membrane complex of the cornea with resultant side effects as mentioned above.
U.S. Pat. No. 4,903,695, Warner at. al., issued Feb. 27, 1990 disclosed a method of performing Barraquer's keratomileusis operation using an ultraviolet or infrared laser to effect the tissue modification step, thereby replacing the cryolathe and BKS device. It also circumvents laser damage to the anterior cornea. However, the method requires the use of a mechanical microkeratome to first detach a circular disc of tissue from the patient's cornea. Following this mechanical cut, the laser irradiation is applied selectively to the cut stromal surface left behind on the patient to remove tissue in a controlled fashion such that when the initially resected disc is replaced onto the bed from which it was removed, a new curvature is imposed onto the anterior corneal surface.
The techniques described above have met with several shortcomings, as partly described. When the laser is used to remove a disc of scarred tissue from the patient's cornea and left to heal (called phototherapeutic keratectomy), this is followed by haze and hyperplasia of the epithelium, which causes undesirable hyperopia. Also, removal of deep pathology may cause greater haze and corneal instability, and is usually not attempted. The current invention solves both problems by restoring corneal thickness to approximately normal and providing an anterior membrane complex.
When the laser is used as above in Warner, et. al., to correct an optical error, the surgeon must use a microkeratome to first prepare the patient's cornea in anticipation of laser ablation. This instrument has been shunned by most surgeons who have used it due to technical difficulty in mastering it, irregular cuts, and deleterious visual sequellae in some cases.
The present invention allows for the performance of phototherapeutic and photorefractive keratectomy without the need for any complex mechanical cutting device, such as the microkeratome, in patient surgery while simultaneously providing a normal anterior membrane complex. To date, this has not been accomplished.